Merge pull request #11634 from vpisarev:empty_mat_with_types_2

fixes handling of empty matrices in some functions (#11634)

* a part of PR #11416 by Yuki Takehara

* moved the empty mat check in Mat::copyTo()

* fixed some test failures

modules/core/include/opencv2/core/mat.inl.hpp

@@ -1673,7 +1673,7 @@ Mat_<_Tp>& Mat_<_Tp>::operator = (const Mat& m)
     {
         return (*this = m.reshape(DataType<_Tp>::channels, m.dims, 0));
     }
-    CV_DbgAssert(DataType<_Tp>::channels == m.channels());
+    CV_Assert(DataType<_Tp>::channels == m.channels() || m.empty());
     m.convertTo(*this, type());
     return *this;
 }

modules/core/src/arithm.cpp

@@ -1233,6 +1233,12 @@ void cv::compare(InputArray _src1, InputArray _src2, OutputArray _dst, int op)
     CV_Assert( op == CMP_LT || op == CMP_LE || op == CMP_EQ ||
                op == CMP_NE || op == CMP_GE || op == CMP_GT );
 
+    if(_src1.empty() && _src2.empty())
+    {
+        _dst.release();
+        return;
+    }
+
     bool haveScalar = false;
 
     if ((_src1.isMatx() + _src2.isMatx()) == 1

modules/core/src/convert.cpp

@@ -1304,6 +1304,12 @@ void cv::Mat::convertTo(OutputArray _dst, int _type, double alpha, double beta)
 {
     CV_INSTRUMENT_REGION()
 
+    if( empty() )
+    {
+        _dst.release();
+        return;
+    }
+
     bool noScale = fabs(alpha-1) < DBL_EPSILON && fabs(beta) < DBL_EPSILON;
 
     if( _type < 0 )

modules/core/src/copy.cpp

@@ -246,13 +246,14 @@ void Mat::copyTo( OutputArray _dst ) const
         return;
     }
 
+    if( empty() )
+    {
+        _dst.release();
+        return;
+    }
+
     if( _dst.isUMat() )
     {
-        if( empty() )
-        {
-            _dst.release();
-            return;
-        }
         _dst.create( dims, size.p, type() );
         UMat dst = _dst.getUMat();
         CV_Assert(dst.u != NULL);